Wednesday, February 24, 2010

130' vs 110' for Multiband Doublet Antenna

See this document for a first pass analysis of the antenna choices that W4BXI is considering.

Saturday, February 13, 2010

W1TP Telegraph & Scientific Instrument Museums

Friday's snow in Birmingham was not sufficient to keep folks away from an excellent presentation by Bell Ringer #263 about the history and technology of the German Enigma cipher machine. A reference in Keith's presentation contains a video that reenacts the use of the machine during WWII. 

A visit to the W1TP home page reveals a treasure trove of information and photos of interest to collectors and historians. The focus is on telegraph equipment and scientific instruments and the Enigma. One of his web pages contains some nice photos from the 2009 Dayton Hamfest.


Tuesday, February 9, 2010

75 m Loop Antenna at W4UOA

Corrected version -- original had results for double the intended loop length.
Here is some analysis of a loop antenna proposed by W4UOA. The following slide show presents impedance vs frequency for several bands. Resistance and reactance are plotted in the upper half of each slide, and impedance magnitude and phase are in the lower half. Click on any slide to view it in the source album. Additional magnification is available using the magnifier icon in the Picasa album view.

The radiation patterns below show the typical progression in frequency, with more lobes and lower angle of radiation as frequency increases. There is a large amplitude difference between the peaks and nulls in the patterns at higher frequencies.

The antenna elements and support wires are the silver lines. The feedline is blue. The color-coded radiation pattern was left at original scale to show its relationship to the antenna structure. The program allows zooming the pattern much larger, such that the antenna structure is engulfed. Viewing at any azimuth and elevation angle, in increments of 5ยบ, is available. Standard 2-D plots are also available.

The predicted performance of this antenna seems consistent with other published analyses of loop antennas, and does not appear to be adversely affected by un-grounded metallic support wires.

Thursday, February 4, 2010

Radio Estate Sale for Oren Anderson, W4HDF

KE4ID is in the process of posting items for Oren's estate sale. You can view available items on this page of the Birmingham Crystal Radio Group web site. Check back often to see additional items as they are added.